In recent years, flexography has been attracting attention with packing being modernized. However, a process for preparing a conventional flexographic printing plate requires at least three steps of (a) preparing a metal plate, (b) molding and (c) vulcanizing rubber. The defects with this process are therefore that it requires skilled workmanship and a long period of time and that the preparation requires a considerably high cost. As a material to overcome these defects, there have been developed printing plates of photosensitive resins developable with a solvent, and a flexographic printing plate can now be simply prepared. Since, however, these printing plates are formed of diene-containing rubbers such as polybutadiene as a base material, it is required to use halogen-containing solvents such as trichlene, perchlene, etc., as a developer in development. Nevertheless, these halogen-containing solvents tend to be limited in use due to an environmental problem and toxicity to human bodies. It has been therefore desired to develop a flexographic printing plate which can be developed with water, free of toxicity to a human body and which has resistance to a water-base ink used for flexography. However, the prior art has found it difficult to satisfy contradicting requirements, i.e., water-developability and resistance to water and alcohol. The present inventor has therefore made a study to apply a microgel obtained by the novel process for producing a photosensitive microgel (JP-A-02-263805), proposed by the present applicant, to a flexographic printing plate. However, it has been hardly possible to obtain a satisfactory one in terms of physical properties such as rubbery resilience.
Further, the present inventor has produced a thick printing plate for flexography by a method of:
(a) repeating casting .fwdarw. drying .fwdarw. casting, or
(b) gradually drying a thick material around room temperature. However, the problem with these methods is that time and labor are extraordinarily required, and that other components and an initiator to be used are limited to water-base ones.